The invention relates to a wavelength multiplex optical communication module for use in various communication networks, and more particularly to a wavelength multiplex optical communication module for use in multiplexing/demultiplexing or transmission/reception of light with different wavelengths.
Various wavelength multiplex optical communication modules for use in multiplexing/demultiplexing or transmission/reception of light with different wavelengths have been developed.
FIG. 1 is a side view of a conventional wavelength multiplex optical communication module disclosed in Japanese Patent Laid-Open No. 133069/1998. This wavelength multiplex optical communication module 11 comprises a silicon substrate 12 and an optical waveguide 14 mounted on the silicon substrate 12 in its upper surface 13. An input/output (hereinafter often referred to as xe2x80x9cI/Oxe2x80x9d) port optical fiber 16 is provided on the left side of the optical waveguide 14 in the drawing so that one end of the I/O port optical fiber 16 is connected to a port 15 in the optical circuit. An optical fiber 17, a photodiode (PD) module 18, and a laser diode module 19 are provided on the right side of the optical waveguide 14 in the drawing. In FIG. 1, the photodiode module 18 is hidden by the laser diode module 19. Numeral 21 designates a core of the I/O port optical fiber, numeral 22 a core of the optical fiber 17, and numeral 25 an I/O port.
FIG. 2 shows the upper surface of this conventional wavelength multiplex optical communication module. As shown in FIG. 2, the core 21 of the I/O port optical fiber 16 and the core 22 of the optical fiber 17 are provided on an extension line of an identical optical axis. Light with different wavelengths xcex1 and xcex2 is incident through the I/O port optical fiber 16 on the port 15. The incident light is demultiplxed in a multiplexing/demultiplexing section 24 in the optical circuit within the optical waveguide 14, and the demultiplexed light with wavelength xcex1 as such travels straight and is sent to the optical output port 25. One end of the optical fiber 17 is optically coupled to the optical output port 25, and the light with wavelength xcex1 is guided through the core 22 of the optical fiber 17.
On the other hand, the light with wavelength xcex2 demultiplexed in the multiplexing/demultiplexing section 24 is branched in a branching section 26 into two parts which travel in two respective directions. One of the branched light parts reaches a port 27 and is input into a photodetector 18 where the optical signal is converted to an electrical signal. The other branched light part reaches a port 28. A laser diode (LD) module 19 is connected to the port 28. The laser diode module 19 is constructed so as to output the light with wavelength xcex2. This light travels in the reverse direction through the branching section 26 and reaches the multiplexing/demultiplexing section 24 for multiplexing. The multiplexed light is input through the port 15 into the I/O port optical fiber 16 and is guided through the core 21 in the reverse direction.
The wavelength multiplex optical communication module 11 shown in FIGS. 1 and 2 has a structure such that the optical waveguide 14, the photodiode module 18 for receiving an optical signal, and the laser diode module 19 for sending an optical signal are mounted on the upper surface 13 of one silicon substrate 12. By virtue of this structure, the wavelength multiplex optical communication module 11 can be prepared at low cost.
In this wavelength multiplex optical communication module 11, two optical fibers 16, 17 are provided respectively on both sides of the optical waveguide 14 so as to sandwich the optical waveguide 14 therebetween. Therefore, in order to prevent the optical fibers 16, 17 from contacting with other electrical components (not shown), a certain space should be provided on both sides of the wavelength multiplex optical communication module 11. This disadvantageously makes it difficult to realize high density packaging of the wavelength multiplex optical communication module 11.
Japanese Patent No. 2919329 and Japanese Patent Laid-Open No. 333243/1993 also disclose wavelength multiplex optical communication modules. Also in these techniques, optical fibers are connected to an optical waveguide respectively in its end faces opposite to each other. Therefore, these techniques involve the same problem as the technique shown in FIGS. 1 and 2.
FIG. 3 shows a wavelength multiplex optical communication module which has been proposed in Japanese Patent Laid-Open No. 190026/1996 for solving the problem of packaging density of the above wavelength multiplex optical communication modules. In this conventional wavelength multiplex optical communication module 31, one end of an input single mode optical fiber 32 and one end of an output optical fiber 33 are coupled through a glass block 34 respectively to corresponding I/O ports 36, 37 of the optical waveguide 35. Light with different wavelengths xcex1 and xcex2 is incident through the input single mode optical fiber 32 on the I/O port 36. The light with wavelengths xcex1 and xcex2 is incident on a dielectric multi-layer film 39 disposed in a groove 38 formed in the center portion of the optical waveguide 35. Light with wavelength xcex1 as such passes through the dielectric multi-layer film 39 and, in a branching section 41, is branched into two parts which travel through two respective paths. A laser diode module 42 is optically connected to the end of one of the paths, and a photodiode module 43 is optically connected to the end of the other path.
In this conventional wavelength multiplex optical communication module 31, the dielectric multi-layer film 39 is disposed perpendicularly to a reference plane 45 in a planar optical waveguide circuit to simplify the structure and thus to prepare a compact module. In the prior art technique shown in FIGS. 1 and 2, since two optical fibers 16, 17 are mounted respectively on different end faces of the optical waveguide, high density packaging of the wavelength multiplex optical communication module 11 cannot be realized. On the other hand, the wavelength multiplex optical communication module 31 shown in FIG. 3 solves this problem by connecting the optical fibers 32, 33 to an identical end face.
FIG. 4 shows a wavelength multiplex optical communication module disclosed in Japanese Patent Laid-Open No. 160952/1998 which is another example of the wavelength multiplex optical communication module wherein, as with the prior art technique shown in FIG. 3, two optical fibers are connected to one end face of an optical waveguide. In this wavelength multiplex optical communication module 51, a difference in level is provided in an optical waveguide substrate 52, and the end of a first optical fiber 53 and the end of a second optical fiber 54 are disposed in this portion of the difference in level. Light with different wavelengths xcex1 and xcex2 is incident through the first optical fiber 53 on a corresponding first port 55, is guided through a first optical waveguide 56, and is incident on a wavelength demultiplexing element 58 disposed on a second port 57 which is located opposite to the first port 55 of the optical waveguide substrate 52.
The wavelength demultiplexing element 58 substantially completely reflects light with wavelength xcex1. Therefore, the light with wavelength xcex1 is guided through a second optical waveguide 59, reaches a third port 61, and then is incident on the second optical fiber 54. Further, the wavelength demultiplexing element 58 permits a part of light with wavelength xcex2 to pass therethrough, and this light is received in a photodetector 66 for an optical output monitor provided behind the wavelength demultiplexing element 58. Light with wavelength xcex2, which has been reflected by the wavelength demultiplexing element 58, travels through the first optical waveguide 56 in the reverse direction and is incident on the first optical fiber 53. The light with wavelength xcex2 output from a laser diode module 63 disposed near the second optical fiber 54 is incident through a fourth port 64 on a third optical waveguide 65, is passed through the wavelength demultiplexing element 58, and is received in the photodetector 66 for an optical output monitor.
As described above, in the wavelength multiplex optical communication modules 31, 51 shown in FIGS. 3 and 4, since the two optical fibers 32, 33 or the two optical fibers 53, 54 are mounted on an identical end face, high density packaging can be realized. In the wavelength multiplex optical communication module 31 shown in FIG. 3, however, very troublesome work should be done for inserting a filter of the dielectric multi-layer film 39 (hereinafter referred to as xe2x80x9cdielectric multi-layer film filterxe2x80x9d) into a narrow groove 38 provided in the optical waveguide 35. This disadvantageously makes it difficult to reduce the assembly cost of the module.
In the wavelength multiplex optical communication module 51 shown in FIG. 4, the wavelength demultiplexing element 58 responsible for complicate selection of transmission and reflection should be used, and, consequently, the production cost of the module is disadvantageously increased. Further, in this wavelength multiplex optical communication module 51, a dielectric multi-layer film for folding back light with a specific wavelength to the outside of the system should be provided on one side of a half mirror in its side on which light is incident. In this example, the dielectric multi-layer film used substantially completely reflects light with wavelength xcex1 while light with wavelength xcex2 is transmitted therethrough. In this case, the light with wavelength xcex1 is reflected from the dielectric multi-layer film, and the light with wavelength xcex2 is reflected from the half mirror. This causes a deviation in light folding-back position of the light with wavelength xcex1 and the light with wavelength xcex2. Disadvantageously, the deviation of the folding-back light from the waveguide increases the loss of light with wavelength xcex2, which has been emitted from the laser diode module 63 as a light emitting device and reflected from the half mirror, and the proportion of light led to the first optical fiber 53 is reduced. Further, since the dielectric multi-layer film is provided on one side of the half mirror, a warp disadvantageously occurs in the dielectric multi-layer film filter, leading to lowered performance of the filter.
Accordingly, it is an object of the invention to provide a wavelength multiplex optical communication module which can realize various functions, such as transmission and reception of signal light of a plurality of wavelengths, in a simple construction.
The above object can be attained by the following features of the invention.
(i) A wavelength multiplex optical communication module comprising: (a) a light emitting device disposed on an optical waveguide substrate; (b) a first optical waveguide for guiding signal light with a first wavelength output from said light emitting device; (c) a second optical waveguide that has a path connecting one end face of the optical waveguide substrate to the other end face of the optical waveguide substrate and has a portion of the waveguide, between both ends of the path, which is disposed closely to the first optical waveguide to constitute a directional coupler for transferring the power of the signal light with a first wavelength at a predetermined ratio to the second optical waveguide; (d) a wavelength filter disposed at said other end face of the optical waveguide substrate, for reflecting the signal light with a first wavelength and, in addition, permitting signal light with a second wavelength different from the first wavelength to be transmitted therethrough; (e) a third optical waveguide that has a path connecting one end face of the optical waveguide substrate to the other end face of the optical waveguide substrate and is disposed in such a manner that the end of the third optical waveguide and the end of the second optical waveguide face the wavelength filter on said other end face side of the optical waveguide substrate so that, according to reflecting characteristics of the wavelength filter with respect to a predetermined wavelength, a reflected light, which has been guided through the second optical waveguide and reflected from the wavelength filter, is coupled to the third optical waveguide while a reflected light, which has been guided through the third optical waveguide and reflected from the wavelength filter, is coupled to the second optical waveguide; and (f) an out-of-substrate photodetector that is provided outside the optical waveguide substrate so as to face said other end face of the optical waveguide substrate through the wavelength filter and receives the signal light with a second wavelength which has passed through the wavelength filter.
The above item (i) corresponds to the first, fifth, or sixth preferred embodiment of the invention which will be described later. According to this construction, the signal light with a first wavelength output from a light emitting device is guided through a first optical waveguide, and the power of this light is transferred by the directional coupler to the second optical waveguide, and the light can be led through the second optical waveguide to the outside of the module. The proportion of the power of the signal light with a first wavelength to be transferred to other optical waveguide by the directional coupler may be 100% or around 100%. When the signal light is divided according to applications, design may be done so that a desired transfer proportion can be provided. One end of the second optical waveguide and one end of the third optical waveguide are disposed at one end face of the optical waveguide substrate, while the other end of the second optical waveguide and the other end of the third optical waveguide are disposed so as to face the wavelength filter at the other end face of the optical waveguide substrate. By virtue of this construction, according to the characteristics of the wavelength filter, signal light with a second wavelength may be transmitted through the wavelength filter and received in an out-of-substrate photodetector, or light reflected from the wavelength filter may be optically coupled to the second optical waveguide or the third optical waveguide for leading the reflected light to the outside of the module. In the wavelength multiplex optical communication module according to item (i), when optical fibers are connected to the wavelength multiplex optical communication module, two optical fibers are disposed only on the above-described one end face side of the optical waveguide substrate. Therefore, various components can be arranged on the other side without any trouble, and this can contribute to improved packaging density of various components.
(ii) The wavelength multiplex optical communication module according to the above item (i), wherein signal light with second and third wavelengths is guided, from the one end face side of the second optical waveguide, through the second optical waveguide.
The above item (ii) corresponds to the first preferred embodiment, which will be described later, and specifies the case where, in the wavelength multiplex optical communication module according to the above item (i), signal light with second and third wavelengths is introduced from the above one end face toward the other end face of the second optical waveguide. In this case, a method for using the module can be adopted wherein signal light with a first wavelength is sent from the wavelength multiplex optical communication module to the outside of the module, light with second and third wavelengths is introduced from the outside of the module into the module, and, in the input light with second and third wavelengths, light with a second wavelength is received while light with a third wavelength is again sent to the outside of the module.
(iii) The wavelength multiplex optical communication module according to the above item (i), wherein the wavelength filter reflects signal light with a third wavelength different from the first and second wavelengths, the signal light with a third wavelength is guided through the third optical waveguide toward said other end face, and the signal light with a third wavelength and the signal light with a first wavelength are output from the second optical waveguide and led to the outside of the module.
The above item (iii) corresponds to the second preferred embodiment which will be described later. In this case, a method for using the module can be adopted wherein signal light with a first wavelength is sent from the wavelength multiplex optical communication module to the outside of the module, signal light with a second wavelength is introduced from the second optical waveguide and is received, and signal light with a third wavelength input from the third optical waveguide is again sent from the second optical waveguide to the outside of the module.
(iv) A wavelength multiplex optical communication module comprising: (a) an on-substrate photodetector disposed on an optical waveguide substrate; (b) a second optical waveguide which has a path connecting one end face of the optical waveguide substrate to the other end face of the optical waveguide substrate and guides signal light with first to third wavelengths different from one another; (c) a first optical waveguide that has a portion disposed closely to the waveguide portion in the second optical waveguide to constitute a directional coupler for transferring the power of signal light with a first wavelength at a predetermined ratio to the second optical waveguide and the end of a guide front of the signal light with a first wavelength is optically connected to the on-substrate photodetector; (d) a wavelength filter disposed at said other end face of the optical waveguide substrate, for reflecting the signal light with a first wavelength and, in addition, permitting signal light with a second wavelength different from the first wavelength to be transmitted therethrough; (e) a third optical waveguide that has a path connecting one end face of the optical waveguide substrate to the other end face of the optical waveguide substrate and is disposed in such a manner that the end of the third optical waveguide and the end of the second optical waveguide face the wavelength filter on said other end face side of the optical waveguide substrate so that, according to reflecting characteristics of the wavelength filter with respect to a predetermined wavelength, a reflected light, which has been guided through the second optical waveguide and reflected from the wavelength filter, is coupled to the third optical waveguide while a reflected light, which has been guided through the third optical waveguide and reflected from the wavelength filter, is coupled to the second optical waveguide; and (f) an out-of-substrate photodetector that is provided outside the optical waveguide substrate so as to face said other end face of the optical waveguide substrate through the wavelength filter and receives the signal light with a second wavelength which has passed through the wavelength filter.
The above item (iv) corresponds to the third preferred embodiment of the invention which will be described later. In this wavelength multiplex optical communication module, the following method for using the module can be adopted. Signal light with first to third wavelengths is introduced from the outside of the module into the second optical waveguide. An on-substrate photodetector is disposed on the first optical waveguide. The power of signal light with a first wavelength input into the second optical waveguide is transferred by the directional coupler to the first optical waveguide and is received in the on-substrate photodetector. Signal light with a second wavelength is transmitted through the wavelength filter and is received in the out-of-substrate photodetector. Signal light with a third wavelength is reflected from the wavelength filter, is guided through the third optical waveguide, and is sent to the outside of the module. Also in this wavelength multiplex optical communication module according to the item (iv), when two optical fibers are connected to the wavelength multiplex optical communication module, the two optical fibers are disposed only on the one end face side of the optical waveguide substrate. Therefore, various components can be arranged on the other end face side without any trouble, and, thus, the packaging density of various components can be improved. (v) A wavelength multiplex optical communication module comprising: (a) a light emitting device disposed on an optical waveguide substrate; (b) a first optical waveguide for guiding signal light with a first wavelength output from said light emitting device; (c) a second optical waveguide that has a path connecting one end face of the optical waveguide substrate to the other end face of the optical waveguide substrate and has a portion of the waveguide, between both ends of the path, which is disposed closely to the first optical waveguide to constitute a directional coupler for transferring the power of the signal light with a first wavelength at a predetermined ratio to the second optical waveguide; (d) a wavelength filter disposed at said other end face of the optical waveguide substrate, for permitting the signal light with a first wavelength to be transmitted therethrough and, in addition, reflecting signal light with a second wavelength different from the first wavelength; (e) a third optical waveguide that has a path connecting one end face of the optical waveguide substrate to the other end face of the optical waveguide substrate and is disposed in such a manner that the end of the third optical waveguide and the end of the second optical waveguide face the wavelength filter on said other end face side of the optical waveguide substrate so that, according to reflecting characteristics of the wavelength filter with respect to a predetermined wavelength, a reflected light, which has been guided through the second optical waveguide and reflected from the wavelength filter, is coupled to the third optical waveguide while a reflected light, which has been guided through the third optical waveguide and reflected from the wavelength filter, is coupled to the second optical waveguide; and (f) an out-of-substrate photodetector that is provided outside the optical waveguide substrate so as to face said other end face of the optical waveguide substrate through the wavelength filter and receives the signal light with a first wavelength which has passed through the wavelength filter.
The item (v) corresponds to the fourth preferred embodiment which will be described later. In the wavelength multiplex optical communication module according to the item (v) the following method for using the module can be adopted. Signal light with a first wavelength guided through the first optical waveguide is transferred by the directional coupler to the second optical waveguide and is sent through the second optical waveguide to the outside of the module. On the other hand, the signal light with a first wavelength and signal light with a second wavelength are introduced from the outside of the module, and, in these lights, the light with a first wavelength is transmitted through the wavelength filter and is received in the out-of-substrate photodetector, while the signal light with a second wavelength is reflected from the wavelength filter, is coupled to the third optical waveguide, and is sent to the outside of the module. Also in this wavelength multiplex optical communication module according to the item (v), when two optical fibers are connected to the wavelength multiplex optical communication module, the two optical fibers are disposed only on the one end face side of the optical waveguide substrate. Therefore, various components can be arranged on the other end face side without any trouble, and, thus, the packaging density of various components can be improved.
(vi) A wavelength multiplex optical communication module comprising: (a) a light emitting device disposed on an optical waveguide substrate; (b) an on-substrate photodetector disposed on the optical waveguide substrate; (c) a first optical waveguide for guiding signal light with a first wavelength output from said light emitting device; (d) a second optical waveguide that has a path connecting one end face of the optical waveguide substrate to the other end face of the optical waveguide substrate and has a portion of the waveguide, between both ends of the path, which is disposed closely to the first optical waveguide to constitute a directional coupler for transferring the power of the signal light with a first wavelength at a predetermined ratio to the second optical waveguide; (e) a wavelength filter disposed at said other end face of the optical waveguide substrate, for reflecting the signal light with a first wavelength and, in addition, permitting signal light with a second wavelength different from the first wavelength to be transmitted therethrough; (f) a third optical waveguide that has a path leading from the on-substrate photodetector to the other end face of the optical waveguide substrate and is disposed in such a manner that the end of the third optical waveguide and the end of the second optical waveguide face the wavelength filter on said other end face side of the optical waveguide substrate so that, according to reflecting characteristics of the wavelength filter with respect to a predetermined wavelength, a reflected light, which has been guided through the second optical waveguide and reflected from the wavelength filter, is coupled to the third optical waveguide while a reflected light, which has been guided through the third optical waveguide and reflected from the wavelength filter, is coupled to the second optical waveguide; and (g) an out-of-substrate photodetector that is provided outside the optical waveguide substrate so as to face said other end face of the optical waveguide substrate through the wavelength filter and receives the signal light with a second wavelength which has passed through the wavelength filter.
The item (vi) corresponds to the seventh preferred embodiment of the invention which will be explained later. In the wavelength multiplex optical communication module according to the item (vi), the following method for using the module can be adopted. A light emitting device and an on-substrate photodetector are disposed on the optical waveguide substrate. Signal light with a first wavelength output from the light emitting device is transferred by the directional coupler to the second optical waveguide and is sent through the second optical waveguide to the outside of the module. Signal light with second and third wavelengths is introduced from the outside of the module into the second optical waveguide, and, in the signal light with second and third wavelengths, signal light with a second wavelength is transmitted through the wavelength filter and is received in the out-of-substrate photodetector, while signal light with a third wavelength is reflected from the wavelength filter, is coupled to the third optical waveguide, and is received in the on-substrate photodetector. In this wavelength multiplex optical communication module according to the item (vi), when an optical fiber is connected to the wavelength multiplex optical communication module, one optical fiber is disposed on the one end face side of the optical waveguide substrate. Therefore, various components can be arranged on the other end face side without any trouble, and, thus, the packaging density of various components can be improved.
(vii) The wavelength multiplex optical communication module according to any one of the above items (i) to (vi), wherein a monitoring photodetector for receiving light output from the light emitting device is disposed on the optical waveguide substrate in its position behind the light emitting device provided on the optical waveguide substrate.
The item (vii) corresponds to the fifth preferred embodiment of the invention which will be explained later. In this wavelength multiplex optical communication module according to the item (vii), not only a light emitting device but also a photodetector for monitoring is disposed on the optical waveguide substrate. By virtue of this construction, the power of light output from the light emitting device can be stabilized, and, at the same time, the number of components disposed outside of the optical waveguide substrate can be reduced.
(viii) The wavelength multiplex optical communication module according to any one of the above items (i) to (vi), wherein a monitoring photodetector for receiving light output from the light emitting device is disposed, so as to face the light emitting device disposed on the optical waveguide substrate, in a region on the outside of the optical waveguide substrate wherein the wavelength filter is not interposed between the light emitting device and the monitoring photodetector.
The item (viii) corresponds to the sixth preferred embodiment of the invention which will be explained later. This wavelength multiplex optical communication module according to the item (viii) is different from the wavelength multiplex optical communication module according to the item (vii) in that the photodetector for monitoring is disposed in a region on the outside of the optical waveguide substrate to stabilize the power of light output from the light emitting device.
(ix) The wavelength multiplex optical communication module according to the above item (i), (iii), (iv), (v), (vi), or (viii), wherein the wavelength filter is applied to the end face of the optical waveguide substrate.
In the wavelength multiplex optical communication module according to the item (ix), the wavelength filter is applied to the end face of the optical waveguide substrate. According to this construction, various wavelength multiplex optical communication modules can be simply prepared by selectively using various wavelength filters, and, thus, parts and packages can be shared.